The present invention is generally directed to ink compositions, and more specifically the present invention is directed to ink jet compositions and to processes for the preparation thereof. Accordingly, in an embodiment of the present invention there is provided aqueous ink compositions comprised of polymeric dyes, especially those dyes containing water soluble polymers with highly stable chromophores covalently bonded thereto. The aforementioned ink compositions in addition to possessing improved waterfastness are of a desirable nonfishy odor; possess desirable viscosity values, acceptable surface tension characteristics, improved drying properties; and further, these inks are free of environmental hazards in that they, for example, evidence a negative Ames test and thus are nonmutagenic. Also, the ink compositions of the present invention can be altered by added spreading substances such as benzyl alcohol, thereby enabling increased spot sizes.
Compositions which are useful in ink jet printing systems are well known, and generally contain water soluble dyes. There is thus disclosed, for example, in U.S. Pat. No. 3,846,141 an ink composition useful in jet printing comprised of an aqueous solution of a water-soluble dye; and a humectant material formed of a mixture of a lower alkoxy triglycol; and at least one other compound selected from the group consisting of a polyethylene glycol, a lower alkyl ether of diethylene glycol, and glycerol. According to the disclosure of this patent, the printing inks have the desired viscosity for use in jet printing in that the viscosity of the composition is subjected to little variation with use as water is lost by evaporation during recirculation of the ink composition through the jet printer. Moreover, apparently the humectant system disclosed in this patent substantially prevents or minimizes tip drying of the printing ink in the orifice or nozzle during down time of the printer, such as when the printer is rendered inoperative. As further disclosed in this patent, the basic imaging technique in jet printing involves the use of one or more ink jet assemblies connected to a pressurized source of ink. Each individual ink jet includes a very small orifice usually of a diameter of 0.0024 inches, which is energized by magneto restrictive piezo-electric means for the purpose of emitting a continuous stream of uniform droplets of ink at a rate of 33 to 75 kilohertz. This stream of droplets is desirably directed onto the surface of a moving web of, for example, paper; and is controlled to form printed characters in response to video signals derived from an electronic character generator and in response to an electrostatic deflection system.
Also, there is disclosed in U.S. Pat. No. 4,279,653 ink jet compositions containing water-soluble wetting agents, a water-soluble dye and an oxygen absorber. Similarly, U.S. Pat. No. 4,196,007 describes an ink jet printing composition with an aqueous solution of a water-soluble dye and a humectant consisting of at least one water-soluble unsaturated compound. Further, there is disclosed in U.S. Pat. No. 4,267,088 coatings particularly useful as marking inks wherein there is selected an epichlorohydron--modified polyethylenamine and an ethylene oxide modified polyethylenamine in an aqueous solution. Other prior disclosing aqueous inks for ink jet printing include U.S. Pat. Nos. 4,101,329; 4,290,072; 4,383,859; 4,235,773; 4,279,814; 4,443,371; 4,286,989; 4,299,630; 4,167,393; 3,864,296; 4,238,234; 3,234,025; 4,520,143; 3,920,855; and 4,182,612.
Additionally, there is disclosed in U.S. Pat. No. 4,197,135 ink compositions with improved waterfastness comprised of at least one water soluble dye, and a polyamine with 7 or more nitrogen atoms per molecule. Specifically, there is illustrated in this patent an ink composition comprising an aqueous solution of at least one water-soluble dye, and about 0.5 percent to about 10 percent by weight concentration of a polyamine having 7 or more nitrogen atoms per molecule. In column 1, beginning at line 61, it is indicated that the preferred polyamines have the hydrogen of the primary amine group replaced with either a methyl or a hydroxy ethyl group. Examples of the fully substituted polyamines selected are outlined in column 2, beginning at line 40.
Furthermore, there is disclosed in copending application U.S. Ser. No. (not yet assigned) D/85099 entitled Waterfast Ink Jet Compositions and Process, the disclosure of which is totally incorporated herein by reference, ink compositions comprised of a major amount of water, a hydroxyethylated polyethylenimine polymer, and a dye component, wherein the polymer has incorporated therein from about 65 percent by weight to about about 80 percent by weight of hydroxyethyl groups. Also, copending application U.S. Ser. No. 723,376, the disclosure of which is totally incorporated herein by reference, illustrates an ink jet composition with certain sulfonated trisazo dyes.
Ink compositions for jet printing can be prepared by a number of known methods. Generally, these methods involve dissolving the various dyes, humectants, viscosity control agents, paper fixing additives, surface tension control additives, biocides and anti-oxidants in a known volume of water; followed by adjusting the pH (and concentration) of the solution to a desirable level. In those situations where the pigments selected are not water-soluble, the inks are prepared by standard known milling processes. However, such pigment dispersions are generally not sufficiently stable, accordingly, when incorporated into a printing machine the ink particles tend to agglomerate resulting in the clogging of the small nozzles contained in the ink jet devices.
Although the above compositions may be suitable for their intended purposes, there continues to be a need for improved ink jet compositions and processes thereof. Additionally, there continues to be a need for ink jet compositions which when in use result in excellent optical print densities, and possess very acceptable waterfastness characteristics. Moreover, there continues to be a need for inks that possess nonmutagenic characteristics enabling them to be safely used in ink jet printing processes. Also, there is a need for ink compositions that permit an increase in the spot size of the ink. Furthermore, there is a specific need for nonmutagenic ink compositions with waterfastness of greater than about 80 percent. There also is a need for polymeric dyes for ink jet compositions formulated from the reaction of a sulfonated water soluble dye with a polyethylenimine. Inks with these dyes incorporated therein have, in many instances, improved physical properties of viscosity, surface tension, and pH; and further, the ink rapidly penetrates into paper substrates. Additionally, the aforementioned inks possess exceptional waterfastness as illustrated hereinafter.